Using academic research as a guise, Williams is believed to have traveled in thePhilippines and elsewhere in Southeast Asia to have sex with underage boys, according to the FBI. The bureau said it had identified 10 victims between ages 9 and 17.

Williams was presented to the media in Mexico with his head bowed, with handcuffs applied behind the back and afterwards with his hands covering his face.

"We instructed judicial policemen to look for this person, called Walter Lee Williamsand he was found in Playa del Carmen on the "Primera Sur" street with 60, specifically in a public park. When specifically questioned about his legal status in the country, he was unable to confirm his situation and after identifying his physical traits, they coincided with the person who appears on FBI's site, related to the sexual exploitation of minors," said state attorney general Armando Garcia.

The FBI added Williams to the 10 most-wanted list on Monday. The bureau was offering a $100,000 reward for information leading directly to his arrest.

The bureau uses the most-wanted list, which has been in place since 1950, to draw attention to some of the most dangerous U.S. fugitives. Over the years 469 fugitives on the list have been caught or located.